How the U.S. Government Tests Its Nuclear Bombs

Nuclear test explosion
A nuclear test explosion from April 1954 is shown in this undatelined photo from the U.S. Defense Department. There's no danger of this cold war of words turning hot. Reuters Pictures

Newsweek published this story under the headline "The Day the Earth Sank" on February 27, 1984. In light of recent news involving North Korea and its recent threats against the U.S., Newsweek is republishing the story.

"I felt the earth shake and before I knew it I was standing on my head. We were walking on the ground and all of a sudden it wasn't there."

For J. L. Smith and 13 other atomic engineers and technicians, an underground nuclear test in Nevada last week produced unexpected fallout: a fall-in. Three hours and 13 minutes after the Department of Energy detonated a nuclear bomb at the Rainier Mesa test site, 90 miles northwest of Las Vegas, a plot of land 60 feet wide and 150 feet long collapsed like a giant sinkhole, dropping more than 30 feet in some places. Test workers and the trailers to which they had returned to collect data from the explosion dropped with it. One of the 14 technicians caught in the cave in suffered serious injuries.

Rattle: The Nevada desert is full of geological dimples from such underground blasts, but this is the first collapse at Rainier Mesa, where 15 such tests have been conducted since 1962. The detonation occurred 1, 168 feet below the surface in a branch of a mile-long tunnel drilled into the side of the mesa (diagram). Before the test, geologists and other scientists had concluded that layers of 10 million- to 15 million-year-old volcanic rock overlying the detonation point would withstand the blast. But the rock was weaker than the experts estimated, perhaps because it contained an unseen fault line between rock layers deposited by different volcanic eruptions. In fact, says Paul Orkild of the U.S. Geological Survey, "the blocks [of rock] do rattle at times." Alternatively, a zone of weakness might have been created within a single layer when rocks here cooled at different rates. This produces what geologists call a "cooling joint," somewhat analogous to the cracks created in a glass when parts of it are heated.

After the blast, the yield of the bomb quickly became the subject of a minor international dispute. A seismograph in Golden, Colo., 750 miles from the point of detonation, registered 4.9 on the Richter scale -- about as strong as a mild earthquake and well within the range of previous tests. A Department of Energy spokesman said the bomb yielded less than 20 kilotons. But the Soviet Union was suspicious: Tass, the official news agency, issued a statement accusing the United States of violating two unratified treaties limiting underground nuclear tests to explosions of less than 150 kilotons.

X-Rays: The Department of Energy emphasized that no radiation leaked from the collapsed mesa. The experiment is designed so that as soon as the bomb is detonated concrete and metal doors slam shut in the branch tunnel; containment has been so effective that visitors can enter the main tunnel. The purpose of the tests is to measure the ability of military hardware such as communications equipment and missile nose cones, which are placed in the branch tunnel, to withstand radiation from nuclear blasts. By analyzing the data the Pentagon believes it can judge whether the neutrons, gamma rays and X-rays generated by an enemy's first strike would so disable American missiles, even if they had already been launched from their silos, that a counterattack would fail. If the retaliatory missiles' guidance systems were sufficiently skewed, for example, they would badly miss their targets. The Department of Energy says it will continue such tests at the Nevada site -- but only after another geological reconnaissance.